Building materials of predetermined lengths are frequently cut from elongate workpieces, also known as beams. Typically, the workpieces are made of wood or wood laminates, aluminum, or plastic, such as plastic laminate formed from polyvinyl chloride.
The most common way for cutting a workpiece into one or more predetermined lengths is to first trim one end of the workpiece to a satisfactory shape. The predetermined length or lengths is then measured relative to the shaped end for cutting. Typically, a circular saw machine or a band saw machine is used for the cutting. However, since these saw machines are not dedicated to cutting workpieces to predetermined lengths, the use of such machines in the foregoing way is extremely inefficient and laborious because a number of machining processes and manual operations are required.
An attempted solution in increasing the efficiency of using circular saw or band saw machines in cutting workpieces to predetermined lengths is the conventional cutting apparatus 105 shown in FIG. 6. Specifically, the finishing apparatus 105 includes two circular saws 101 and 102, which are adapted to be installed in parallel with their rotating surfaces being spaced apart by a predetermined distance L. A workpiece 103 is fed into the apparatus 105 along split lines of cutting circumferences of the circular saws 101 and 102 for simultaneously cutting both ends of the workpiece 103 to obtain building material of a predetermined length. With the conventional apparatus 105, a sequence of operations including feeding, cutting and discharge of a material are all mechanically associated with each other and sequentially performed on the same plane and in the same direction.
In the conventional apparatus 105, the workpiece 103 is supported by a pair of dogs 111 and 112 protrusively formed on two chain conveyers 109 and 110 which are disposed in a parallel, spaced-apart relationship. For cutting the workpiece 103 to form end surfaces 106 and 107 perpendicular to the major axis 108, the workpiece 103 must be supported so as to constantly direct the major axis 108 perpendicular to the rotating surfaces of circular saws 101 and 102.
To do so, the dogs 111 and 112 supporting the workpiece 103 at both ends thereof must always be kept in-phase. For preventing the dogs 111 and 112 from falling into an out-of-phase condition, driving chain wheels 115 and 116 for driving the two chain conveyers 109 and 110 are linked by a rigid shaft 118 having a key groove 117. However, the dogs 111 and 112 may be displaced due to unequal stretching of the chain conveyers 109 and 110 over time. Thus, it is necessary to adjust the positions of the dogs 111 and 112 at relatively frequent intervals to compensate for unequal stretching of the chain conveyers 109 and 110. Furthermore, since these machine elements are all mechanically linked with each other and mutually act in association, adjustment of the dogs 111 and 112 is not easily carried out.
Also, in the conventional apparatus 105 as described above, the workpiece 103 should be clamped during a cutting operation so as to prevent the workpiece 103 from displacing. Thus, forces in the feeding direction and the vertical direction must be always applied to the workpiece 103 while it is being fed into the apparatus 105. For applying such forces to the workpiece 103, a pair of belt conveyers 113 and 114 are provided, which apply downward vertical forces and simultaneously move in a direction parallel to the urging direction. Thus, the belt conveyers 113 and 114 must extend over the whole region of the cutting process and run at the same speed as the chain conveyers 109 and 110. Additionally, since the two chain wheels 115 and 116 are linked together by the rigid shaft 118 having the key groove 117 in order to rotate them in-phase, the whole structure of the apparatus 105 is necessarily large and bulky.
Moreover, often it is desired cut a workpiece 103 into two or more pieces of different lengths, for example, a vertical member and a horizontal member for a door. The conventional cutting apparatus 105 cannot simultaneously cut a single workpiece 103 into a plurality of pieces having different lengths.
Additionally, the conventional cutting apparatus 105 cannot precisely cut a workpiece 103 orthogonal to the major axis 108 of the workpiece to obtain a finished building material product of a predetermined length. More particularly, when a building material product is cut to a satisfactory size and shape, requiring no further machining or cutting, the product is said to be "finished." Referring to FIG. 7(a), the chain conveyors 109 and 110 convey the workpiece 103 in the direction indicated by the arrows for cutting by the circular saw 101. As the chain conveyors 109 and 110 convey the workpiece 103 past the circular saw 101, the saw cuts the workpiece.
To obtain a finished product, the circular saw 101 must be tilted by a small angle a relative to a cutting line c to maintain a small gap .delta. between the cutting line c and a tail end 101b of the circular saw 101 as shown in FIG. 7(b). Otherwise, a cut surface 103a having been cut by a leading end 101a of the circular saw 101 would be contacted again by the tail end 101b of the circular saw 101 and roughed thereby. Tilting the circular saw 101 by the angle .alpha. causes the cut surface 103a' of the workpiece 103' on the other side of the circular saw 101 to be roughed.
Also, the conventional apparatus 105 is not capable of obliquely cutting a workpiece at a substantial angle. Hence, the conventional apparatus 105 has several drawbacks that are especially disadvantageous for industrial use.
The present invention provides an improved solution for cutting building products of different lengths from elongate workpieces.